A wide variety of electrical power converters are available to convert electrical power that is in one form, such as an AC supply, into another from, such as one or more DC voltages. The efficient performance of an electrical power converter depends on many factors, including the operating temperature of the converter. Excessive operating temperatures can lead to a number of problems with the performance of a power converter. For example, excessive temperatures can result in the power converter having a shorter lifetime or an increased likelihood of "thermal shutdown." In practice, the mean-time-between-failure ("MTBF") of a power converter is roughly proportional to the exponential of the temperature at which the converter is operated.
Power converters commonly are coupled in parallel to provide increased power to a single load. In such cases, it is difficult to control the temperature of each power converter within the parallel system. For example, where a number of power converters are cooled by a fan, a temperature gradient may develop which causes the power converters relatively far from the fan to operate at a higher temperature. It is also possible that, due to the particular circuit configuration, certain power converters may supply more power to the load than other power converters. This imbalance in power provided to the load can result in a temperature variation in the converters because the temperature of a power converter is related to the power dissipated in that converter, which is a function of the power provided by the converter.
To assist in regulating the temperature of a parallel system of power converters, control circuits for balancing the power supplied by each power converter to the load may be used. In one type of control circuit, each converter compares its own output current with the average output current of all converters in the system and changes its output voltage such that its output power approximates the average output power of the converter. The problem with this approach is that the temperature of one or more power converters may still rise to a level that will reduce the MTBF of the converter and/or bring it into thermal shutdown as a result of temperature imbalances that are caused by factors other than the imbalance in power supplied to the load.
Accordingly, there is a need for temperature share scheme for controlling the temperatures of power converters operating in parallel to increase the MTBF of the power converters and reduce the risk of thermal shutdown.